Hi, can i know how to find the orientation of an object?

I need to do a project that can identify the position and orientation of object on the conveyor so that the object will be in a right position/posture before being grab by the robotic arm.

Can anyone help me with the algorithm and the development of coding?

Answer 1

[DGM]

Well, here's this. It's not robust, but then again, the test image isn't a real process image either, so I'm going to consider it fair play.

inpict = imread('boxconvey.jpg');

% preprocess
inpict = imflatfield(inpict,20);

% binarize
mkrange = [0 1; 0.192 0.409; 0.742 1];
hsvpict = rgb2hsv(inpict);
M = all(hsvpict >= permute(mkrange(:,1),[2 3 1]),3) ...
    & all(hsvpict <= permute(mkrange(:,2),[2 3 1]),3); 
M = imfill(M,'holes');
M = imopen(M,ones(3));
M = imclose(M,ones(11));

imshow(M)

% get properties
S = regionprops(M,'centroid','image');
C = vertcat(S.Centroid);
numobj = numel(S);

% find number of apparent convex vertices
L = bwlabel(bwperim(M));
thest = zeros(numobj,1);
for k = 1:numobj
    % calculate the object radius, sorted by angle
    [y x] = find(L==k);
    dv = [x y] - S(k).Centroid;
    r = sqrt(sum((dv).^2,2));
    th = atan2d(dv(:,2),dv(:,1));
    [th idx] = sort(th);
    r = r(idx);
    
    % peak finding will probably be fragile
    % good luck with that
    [pk idx] = findpeaks(r,'minpeakprominence',8);
    pkth = th(idx);
    thest(k) = -mean([max(pkth(pkth<0)) min(pkth(pkth>=0))]);
end

thest

thest = 6×1

15.9395 -13.5102 -10.8771 9.6239 -29.9191 29.2230

% demonstrate that the estimated angles are approximately correct
% by counter-rotating the object images
testimgs = cell(numobj,1);
for k = 1:numobj
    th = thest(k);
    thisimg = S(k).Image;
    testimgs{k} = imrotate(thisimg,-th,'crop');
end
montage(testimgs)

I'm sure someone can come up with a better alternative, so I'll leave that to them.

[Nurul Farhana Mohd Fadzli]

Thank you so muchh its really helpful. But about the last part, can you help me on how to get the angle of deviation of each object instaed of correctioning their position?

[DGM]

The vector thest is the angle by which each box appears to be rotated (in degrees).

[Nurul Farhana Mohd Fadzli]

How can i add the bounding box?

[Image Analyst]

You can use plot() to plot lines between the vertices.

[DGM]

You just get the bounding boxes from regionprops() and plot them.

inpict = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/996520/boxconvey.jpg');

% preprocess
inpict = imflatfield(inpict,20);

% binarize
mkrange = [0 1; 0.192 0.409; 0.742 1];
hsvpict = rgb2hsv(inpict);
M = all(hsvpict >= permute(mkrange(:,1),[2 3 1]),3) ...
    & all(hsvpict <= permute(mkrange(:,2),[2 3 1]),3); 
M = imfill(M,'holes');
M = imopen(M,ones(3));
M = imclose(M,ones(11));

S = regionprops(M,'centroid','image','boundingbox');
C = vertcat(S.Centroid);
numobj = numel(S);

% find number of apparent convex vertices
L = bwlabel(bwperim(M));
thest = zeros(numobj,1);
for k = 1:numobj
    % calculate the object radius, sorted by angle
    [y x] = find(L==k);
    dv = [x y] - S(k).Centroid;
    r = sqrt(sum((dv).^2,2));
    th = atan2d(dv(:,2),dv(:,1));
    [th idx] = sort(th);
    r = r(idx);
    
    % peak finding will probably be fragile
    % good luck with that
    [pk idx] = findpeaks(r,'minpeakprominence',8);
    pkth = th(idx);
    thest(k) = -mean([max(pkth(pkth<0)) min(pkth(pkth>=0))]);
end

% draw bounding boxes
imshow(M); hold on
for k = 1:numobj
    thisbb = S(k).BoundingBox;
    boxx = thisbb(1) + [0 thisbb(3)];
    boxy = thisbb(2) + [0 thisbb(4)];
    plot(boxx([1 1 2 2 1]),boxy([1 2 2 1 1]))
end